Gas turbine engines are frequently used in high performance aircraft. The performance requirements for these types of turbine engines are continually being improved, thereby requiring higher operating temperatures. As an example, the combustion chamber, which to date has been required to maintain strength at temperatures up to about 1300.degree.-1400.degree. F., is now being designed to operate at temperatures of about 1600.degree. F. or greater where creep is critical.
In the past, the combustion liners for use within the combustion chamber were manufactured from conventional cobalt-based or nickel-based alloys, such as the widely used Hastelloy X material available from Haynes International Co. These materials were chosen because of their sufficient strength and physical characteristics on conventional cooling ring stiffened designs. These conventional designs are fabricated from sheet stock or alternatively machined from wrought material. However, these techniques can be relatively expensive due to the extensive working required to form the thin-walled cylindrical shape of the combustion liner and because of the number of structural welds required.
Regardless of the method used to form the combustion liners from these conventional materials, a significant shortcoming exists in that these conventional wrought materials do not possess the strength or creep resistance necessary to operate satisfactorily at temperatures of about 1600.degree. F.
High strength, creep-resistant materials are known in the industry which would be suitable for use in the combustion liner at operating temperatures ranging from ambient up to about 1700.degree. F., an example being nickel-based superalloy GTD 222 available from General Electric Company. Such a high strength material is characterized by approximately twice the strength at 1600.degree. F., as compared to the conventional materials currently used to form the combustion liners.
However, until now, there has not been a satisfactory means for manufacturing a thin-walled, close tolerance and cylindrically-shaped combustion liner from this material. The conventional techniques for forming a combustion liner from a cast high strength, high temperature material, such as this, are unacceptable. Acceptable casting methods are unknown. In addition, current technology is unproven with regards to the workability of the material in a wrought condition.
Therefore it would be advantageous to provide means for manufacturing a combustion liner from such a high strength, creep resistant material so as to be useful in the combustion chamber of a gas turbine engine, even when operating at temperatures of about 1700.degree. F. Further, it would be advantageous if such a combustion liner were formed by a method which produced a homogeneous and controlled metallurgical grain structure, so as to optimize the mechanical properties of the material.